Pulse tracking system



April 16, 1957 w. M. slLHAvY PULSE TRACKING SYSTEM 2 Sheets-Sheet 1Filed Feb. 25, 1942 INVENTOR WHITNEY M. SILHAVY ATTORNEY April 16, 1957w. M. slLHAvY 2,789,284

PULSE TRACKING SYSTEM f Filed Feb. 25, 1942 2 Sheets-Sheet 2 F IG.2 A Awc-,.3 To Hao QH [o H50 ai l B A T* 2.71-.. v C H9 BNQ I9 2| -21 2 22 DB-). C U V 4 n 22 22 `G F IT I I/ sa -ss 5%" INVEN-roR K WHITNEY M.ySILHAVY f 3o Aso BY -.-55.91-

f//fmzz K ATTORNEY PULSE TRACKING SYSTEM Whitney M. Silhavy, Mineola, N.Y., assignor to Sperry Rand Corporation, a corporation of DelawareApplication February 25, 1942, Serial No. 432,290

6 Claims. (Cl. 343--7.3)

The present invention is related to the art including dis tancemeasuring devices. Such devices may be used as absolute altimeters wheninstalled on aircraft, for determining the exact distance between craftand ground, or may be used for determining the distance to any desiredobject, as in determining the distance from a iixed station or a surfacevessel to an airplane, surface vessel or other object. v

The present invention is concerned with a device of this type in which apulse preferably of supersonic or electrical high frequency energy isperiodically transmitted toward the object whose distance is to bemeasured, and the waves reflected from the object are received andcompared with the transmitted wave pulse to indicate the distance of thedistant object. In prior devices of this type the received pulse andtransmitted pulse were compared directly to obtain the distanceindication. However, due to extraneous iniiuences, such as multiplereections, atmospheric interference, etc., the received pulse may not bewell defined under some conditions, and leads to ambiguous orindeterminate indications of distance.

According tothe present invention, the received pulse is not useddirectly but is caused to synchronize a suitable electronic device, suchas a multi-vibrator, which thereupon locally generates a voltage pulsewhich may be compared with a similar pulse derived from a transmittedpulse to give the desired indication. Preferably this local pulse is oflixed amplitude and fixed duration. In this manner, since only the timeof arrival and not the amplitude or shape of the received pulse is used,such ambiguous or indeterminate indications are avoided.

Furthermore, in order to minimize noise eects and to be able todifferentiate between several objects which may be reecting wavessimultaneously, or Vbetween mult tiple-reflected pulses, a pulse gate isprovided which effectively passes only the pulse corresponding to thedesired reflecting object. This gate may be manually set to roughly theposition of the chosen received pulse, and thereby indicate an object atthat set distance. Means are also provided to cause this gate to followthe desired pulse even during changes of distance or range, whereby thegate position may roughly indicate distance.

Accordingly, it is an object of the present invention to provideimproved distance measuring devices.

It is another object of the present invention to provide improveddistance-measuring devices of the type wherein periodically recurrentpulses of high frequency energy are radiated and reliected from thedistant object whose distance is to be measured.

It is still another object of the present invention to provide improveddistance-measuring devices of the reflected-pulse type in which theeects of atmospheric interference and stray reflections are minimized oreliminated.

Another object is to provide a direct reading distancemeasuring devicewhich is independent of noise.

It is a still further object of the invention to provide an improveddistance-measuring device of the retiected nited States Patent OPatented Apr. 16, 19757V pulse type in which an adjustable gate isprovided for minimizing the eiect of secondary pulses and atmosphericinterference, this gate being automatically adjusted to cooperate withthe desired received pulse even Vduring changes of distance.

Further objects and advantages of the present invention will be obviousfrom the attached specification and drawings, wherein:

Fig. 1 shows a schematic block wiring diagram of a preferred embodimentof the invention.

Fig. 2 shows a time schedule of the Wave shapes in various portions ofthe circuit.

Fig. 3 shows a similartime schedule for different conditions ofoperation.

Referring to Fig. l, a suitable source of synchronizing oscillations,such as a synchronizing oscillator 1, is provided for generating a waveof suitable low frequency preferably in the audio frequency range, suchas of the order of 2000 cycles. This source of synchronizingoscillations may be of any suitable type, such as a conventionaielectronic oscillator, vibrator, tuning-fork oscillator or a mechanicalalternator, capable of generating put of synchronizing oscillatingsource 1 may have, for

example, the wave shape shown in curve A of Fig. v2

and is fed to a synchronizing pulser 3 of any suitable type adapted topreferably produce short pulses of constant amplitude and a repetitionrate equal to the frequency of the oscillations from source 1. Suchpulses may be of any desired wave` shape, but are preferably very shortin duration in comparison to their period, preferably of the order ofone micro-second in duration. Such pulses are schematically representedby graph B of Fig. 2. These pulses are then applied to a radio orsupersonic transmitter 5 of conventional design to modulate the outputthereof, whereby there is radiated from a suitable supersonic orelectrical high frequency radiator 7 a wave indicated schematically byline 9, and comprising a series of high frequency wave trains with arepetition rate equal to that o f the synchronizing pulses and having anenvelope similar to that of the synchronizing pulses.

These high frequency pulses, upon being reected from an object whosedistance is to be measured, produce a reflected wave indicated at 11which is received in a suitable collector or antenna 13leading to areceiver 15. Receiver 15 may be of any suitable'type for receiving thereflected pulses and obtaining from them an electrical signalcorresponding to the modulation envelope of the received signal, whichmay be as shown in graph'C of Fig. 2. Preferably also a pulse of theproper width and polarity derived from the synchronizing pulser 3 isconnected to receiver 15 as by Way of line 17 to effectively blank outor block thev receiver 15 during intervals in which transmitter 5radiates the transmitted pulses, in order that the relatively highintensity of these transmitted pulses shall not have a harmful effectupon the wave shape of the received wave. If the transmitting system ishighly directional in character, so that substantially none of thetransmitted energy is picked up by the receiver, the blanking pulse maybe omitted.

As shown at 19 in Fig. 2C, this results in zero output during the timeintervals corresponding to the transmitted pulses. The actual reiiectedpulse envelope is indicated at 21 in Fig. 2C and ordinarily will nolonger have the squareV wave shape of the transmitted pulse and will beaccompanied by many smaller pulses such as 23, due to atmosphericinterference and various stray reflections, termed noise In order toeliminate the effect of this noise the output of receiver 15 is fed to astripper 25, which may be comprised of any suitable biased amplifierwhose threshold is set so that only input voltages having 27 of Fig. 2Cwill appear in the output., AAny lother type areaasa magnitude greaterthan that represented by dotted line of'device Vperforming 'the same'function may be used. The output of stripper 25 may be amplified asdesired.

Accordingly,.the output will be as shown .in Fig. 2D, having 'mosttofthenoi'se removed, 'onlythe largerpulses, such as 29, still'.remaii'ng. vIn ordertolremove 'these extraneousp'ulses afurtheramplifier andstripperlis used'havinga threshold corresponding toVdottedilin'e 33 of Fig. 2D, and the output will now be as shown inFigli-3, having iolygpulses 'corresponding .to `the actual .receivedpulses "21.

Some noiserpulses suchas `indicated at`24-in Fig. l2E may also`occur.However, these will occur only at random times with no recurrentregularity and will have no elect on"the circuits to'be described, aswill appear. In order toimprove the. waveshape of these pulses, they arethen transmitted to an amplifier and clipper 35 which may be of anyconventional type amplifier having its upperthreshold set -well'belowthe peak input voltage, wherebythepulsesfzl are clipped and made to.havea steep 'wave' front and Yshort rise -timeas shown in Fig. 2F.These 'reformedpulses are 'now transmitted by Way .ofswitch'i37'in`its'lowerposition to a multi-vibrator 41 of anyconventional type adapted to produce its output vltage pulses -of iixedv.duration .and 'fixed amplitude.

`rMultivihrator 41.1 soadjusted that itis made stable at itsself-.oscillatory .or free-running Yfrequency, just .slightly below `therepetition 'frequency `of the received pulses. 4ln this waythereceived-.pulses will control multivibratorv41 to operate attheirrepetition frequency, Yand random Apulses-such as noisepulsesoro'ther stray pulses, willi-have no effect ont the output ofmultivibrator 41. By

`a suitable balancing circuit or phase shifter, if necessary,

each ofthe output pulses of multivibrator 41 .may be adjusted to beginat the instant .that the vre-shaped reflecteclfpulses .21 reach .themultivibrator.

vThe -most desirable `form of :these output lpulses lis rectangular,asshownat 56 in Fig. 2G, since, as will be seen, this 'leads vto .alinear indication. However, the present inventionisA inno way restrictedonly to rectangular pulses, and, infact, any shape sof l.pulse .may 'beused. The 'output of such .2t-.multivibrator may havev its waveshapeimproved Vto.more nearly approach the vdesirable rectangular .waveshape by means of afurther amplifier-andclipper 43 of the same type -asclipper 35, whoseoutputis now .as shown at 61` in Fig. 2H.`Simultaneouslycither the transmitted pulse Awave envelope asobtainedfrorn.transmitter 5 through a suitable detector or demodulator45, or as obtained directly from the synchronizing pulser 3, havingthe4wave sh-ape 20fshown in Fig. 2B, is fed to a suitable amplifier 47andvthence to a similar multivibrator 49 and amplier and clipper 51 -toproduce-at its output'a similar rectangular or other shape wave-62ofrthesame amplitude andsame duration asthe .output of clipper -43-shownin-Fig. 2H, but of A 'opposite polarity, asshown-in Fig. 2I. Thesetwowaves 61 fand 62 of Figs. 2H and .21am-then amplified in lconventionalamplifiers 53 and 5S having their .outputs Leonnectedfin parallel toa-'common load resistor 57, whereby .the two waves=61 and 62 `of.-Figs.2H and ZI are caused to subtract from. one another, the resultant:appearinglacross output Vresistor 57 in the "form shown at-58 and 59 inFig. 2].

vIt will be clear thatfthe `duration of, for example, the positivepulses59 of Figli depends .upon thetime'interval T between the .transmittedvpulses V20 of Fig. 2B

and-thereceived pulsesll-of'fFig.y 2C. Thus, itthis time interval Tshould decrease, more .of pulses 61 of Fig. 2H will becounter-balancedby thepulse 62 of Fig. ZI,

leaving net output Vpulses 58, 59 as shown in Fig. 2J ofshorterduration. :Alsofif vthis time interval .T increases,

less yof the pulses 61 4-willbe counter-balancedk .and the :resultingfpulsesf 59 will Ybeo'flonger duration.

."Iheoutput voltageappearingfacross resi-Stor 57 issfed` to :afsuitablesnppenjsuchrasva rectifiers, lwhich will pass only the positivepulses 59 and eliminate the negative pulses 58-of the Wave -shown vinFig. 2J. The voltage appearing across the load resistor 65 of thisstripper 63 will therefore have the Wave shape shown at 60 in Fig. 2K,being merely a lseries of unidirectional pulses Whose frequency isfixed, being the repetition frequency of the transmitted pulses, andwhose individual duration is directly proportionaltfor rectangularpulses) to th time interval T-between the transmittedppulse 20 andreceived pulse 21, and therefore directly proportional to the distanceto the distant reflecting object.

In order to give a direct measure of this time T or the distance to thedistant objectythe pulses shown at 60 in Fig. 2K are transmitted toasuitable smoother or lter 67 whose output will therefore be the averageof the pulses 60, shown in Fig. 2K as line 69. It will be clear that theshorter the duration of these pulses 60, the smaller willbe the averageoutput 69, while the longer their duration, thehiglier'w-illbe theaverage output 69, because of .thefix'ed repetition frequency. This'average output "69 'may'therefore besu'itably amplified iniD..l C.amplifier 7 i and mayactuate a suitable indicator 73Whose reading willthenbe directly' proportional to 'and will vary linearly with thedistance to `the distant object to be measured.

If other than rectangular pulses 61, 62 are used, the wave derived inFig/2J will yno lon-ger containpulses whose duration is exactlyyproportional to the time T. Howevcu'in that case, the ,pulses derivedas in 'Fig l2K will have an average value which will correspond directlybut non-linearly tothe timeT. 'Such a non-linear relation may beadvantageous ifit is desired to expand a portion `of the indicated rangeto obtain more sensitive and accurate indicationsl therein.

lIt will be clear Vthat .the system just described effectively measuresthe relative phase between the transmitted and received pulses, .andtherefore .may be used to measure the phase between any two waves.

In place of the indicator-circuit 53, 55, 63, 71, V73Jjustdescribed,.there may be used the device shown in c0- :pending`application Ser. No. 375,373, for Phase Angle Indicator, filed January.22, 1941, in the name of J. E.

Shepherd, now Patent.No. 2,370,692, dated March 6, 1945, which willyyield similar indications.

It vwill therefore be clear that the `device above described has beenmade substantially independent of vatmospheric .interference .and.extraneous vpulses by virtue of the `fact that theactual received.pulse itself is not used for measuring purposes but ismerely used tocontrol suitable-locallygenerated .pulses under the control of theinstant of arrival of the reflectedvpulse.

The system thus far described is verysuitable for determiningthedistance to-the nearest object within the field of the transmitterradiator 7. However, if a series of objectsare within the field, furthermaior pulses may be derived which it may not be .possible to separate bymeans-ofthe strippersy and clippers described.

Thus, referringto VFig. 3, curve A Vcorresponding to Fig. l2Billustrates again =the sequence of transmitted .pulses..20 while curveB, corresponding to Fig. 2Cindicates a representative output of receiver15, this output -being zero during the blankedportions 19 and contain-2Efstill having two major received pulses in each repetition period.'Itis impractical to differentiate bet-Ween these pulses on the basis ofmagnitude alone asis done by the strippers and clipperspespecially soifit is desired to utilize the :smaller-vof -these pulses linstead .ofthelarger.

ln `order toV overcome this diicu'lty 7an adjustable pulse gate isprovided Vwhich willtpass-the .desired 'pulse :and

eliminate the undesired pulse. Thus, referring again to Fig. 1, thesynchronizing oscillator 1 also energizes a suitable variable phaseshifter 75 preferably of the type whose phase shift is controlledproportionately by the rotation of a suitable control member 77 whichmay cooperate with a suitable scale 79 to indicate the amount of thephase shift. This phase shifted voltage is thenpassed through a suitablepulse generator such as 81, of the same type as pulse generator 3, whichderives in its output a wave shape similar to that shown at 83 in Fig.3D. In'this case, the position of these pulses 83 ofFig. 3D isadjustable along the time axis with respect to the transmitted pulses 20or the received pulses 21, 22, by means of the adjustment of phaseshifter 75. These pulses 83 are then passed to a multivibrator 85 ofconventional design, adapted to produce in its output pulses of fixedmagnitude and adjustable duration, synchronized with the input pulses83.` Such pulses are shown at 87 in Fig. 3E and their position relativeto the transmitted pulse 20 or the received pulses 21, 22 is alsoadjustable by means of the phase shifter 75. For this type of operation,switch 37 is thrown to its upper position, whereby the output ofamplifier-clipper 35 having wave shape shown in Fig. 3C is connected toone control grid 89 of a blocking amplifier 91, another of whose controlgrids 93 is suitably coupled to the output of multivibrator 85 havingwave shape 87.

The biases on grids 89 and 93 are so adjusted that tube 91 conducts onlyduring the duration of pulses 87, being non-conductive or blocked at allother times. Hence, by adjusting the time position of pulses 87, as bymeans of phase shifter 75, and by suitably adjusting the duration ofthese pulses, it is possible -to pass only the desired reected pulse,such Vas pulse 22, yWhile suppressing the undesired pulses, such aspulse 21, irrespective of which of these pulses has greater amplitude.

There is thus provided, in effect, a gate permitting the passage ofdesired pulses and suppressing undesired pulses. The output of tube 91will then have the wave shape shown at 22 in Fig. 3F, corresponding toFig. 2F in the situation first described, and the remaining sequence ofoperations is similar to that described above with respect to Fig. 2G,etc.

In operation, the gate 87 may be adjusted in position to correspondroughly to the distance of a selected distant object, as indicated onscale 79. Then the accurate distance may be read from indicator 73, withthe assurance that the effects of noise and other reflected pulses havebeen eliminated.

Also, by suitably adjusting the width of pulse 87 so as to justcircumscribe the desired pulse 22, as may be indicated on a suitablecathode ray indicator, it is possible to approximately read off the timeT, which is proportional to the distance to be measured, from scale 79,since the phase shift produced in phase shifter 75 is exactly the timeinterval T. However, the above device has the objection that it must bemanually adjusted as the distance changes.

In order to avoid this diliiculty, means are provided for automaticallyrepositioning phase shifter 75 as the distance changes. Thus, as hasbeen shown, the adjustment of phase shifter 75 is proportional to thedistance to be measured and therefore would be proportional to the inputto indicator 73, using rectangular multivibrator pulses. Means aretherefore provided for positioning phase shifter 75 proportionately tothe input to indicator 73. Thus, coupled to the control member 77 ofphase shifter 75 as by shaft 76 is a suitable motor 95, shown as beingofthe direct current type having a field 97 permanently energized from aD. C. source such as battery 99. Also energized from battery 99 is acircular potentiometer 101 having a variable arm 103 mechanicallyactuated by shaft 76 but insulated therefrom.

The armature of motor 95 is supplied with a voltage which is equal tothe difference between the output of D. C. amplifier 71 and the portionof potentiometer 101 includes between its variable arm 103 and its fixedgrounded terminal 107. Accordingly, motor 95 will continue to run in theproper direction until the net voltage across its armature has becomezero. In this position, since potentiometer 101 is linearly wound, theangle through whichV shaft 76 has turned will be proportional to thesignal input to terminals 105, and in this way phase shifter will beadjusted proportionately to the time T or the distance to be measured.Hence, the gate provided by pulses 87 is automatically repositioned tomaintain it centralized with respect to its desired received pulse 22.

It Will be clear that any other suitable type of control device may beused in place of motor 95 and its associated circuits for producing thesame function.v In addition, if phase shifter 75 should have anon-linear variation of phase shift with respect to rotation of itscontrol shaft 76, potentiometer 101 may -beNp'rQVided withf'a lsimi-larnon-linear variation of resistance and in this way phase shifter 75 maybe properly actuated despite its non-linear characteristics.

If desired, the mechanical control of phase shifter 775 may be replacedby a suitable electrical control, which may be of the type shown incopending application Serial No. 434,403, for Pulse Receiving System,filed March l2, 1942, in the name of H. M. Stearns.

In operation, the operator will normally throw switch 37 to the downposition. lf the received pulses are ambiguous or indeterminate, as maybe indicated by a suit- 'able cathode ray indicator connected to theoutput of receiver 15, switch 37 may be thrown to the upper position andphase shifter 75 adjusted to the approximate range or distance of theobject it is desired to indicate. Multivibrator is `then `adjusted sothat the duration of its output pulses is short 'enough to eliminateanyundesired pulses, as may be evidenced by a suitable indicator connectedto the output of tube 91. Thereafter the system will automaticallyoperate to indicate the desired distance, while substantiallyeliminating lal1 undesired interfering pulses.

It will be clear that suitable phase Shifters or time delay devices maybe inserted at various points of the circuit to insure the relationshipstated among the various pulses and wave shapes.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

I claim:

l. A radio noise-reducing system operating to eliminate noise that isdisplaced in time with respect to received pulse signals, comprisingmeans for producing gate signals having substantially the same durationas said received signals, utilization means activated by said gatesignals for responding to said received signals, delaying means foradjusting the relative time position of said gate and received signals,and servo motive means for controlling said delaying means in responseto the time position of said received signals.

2. A radio system comprising means lfor transmitting periodic pulsesignals, means for receiving said signals after a time delay, a selfloscillator for producing waves of a frequency :substantially the sameas said received signals, means for generating gate signals havingsubstantially the same duration as said received signals, meansactivated by said gate signals for synchronizing the phase of saidself-oscillator waves to that of said received signals, phase shiftingmeans for adjusting the relative time position of said gate and receivedsignals, and means controlling said phase shifting means in accordancewith the time position of said self-oscillator a'zeaasa .7 waves Vfor:maintaining said -:gate .and lreceived signals concurrent.

43. Afradionoisefreducing system operating to eliminate noise thatisfdisplacedin time with respect to received pulse signals, comprising aself oscillator forproducing waves having afrequency substantially thesame as said received signals, means for generatingi gate signalshavingsubstantially the same duration as sai-dreceive'd signals,.controlling means activated by .said Agate signals for synchronizingthe `phase of said self-oscillator -waves to ythat 4of said'receive'dsignals, phase shifting means for adjusting lthe relative y,time phasek,of said received signals .and said gate signals, and servo moti-vemeans conytrolling `.saidphase shifting means in response tothe timeposition lof saidrself-oscillator waves for maintaining said' gate`signals concurrent 4with said received signals.

4. A dis-tance measuring .radio system comprising means for radiatingperiodic pulse signals, means for receiving said signals afterreflect-ion from an object, va self -oscillator'forproducing waves ofvafrequency substantially the Isameas said pulses, means fOr-generatinggate signals having substantially the same duration as saidr pulses,controlling. means activated by said gate signals for synchronizing thephase .of said self-oscillator waves to that of said receivedxsignals,delaying means for adjustingtherelative timephase of sai-d gate andreceived signals, .phase measuringmeans for measuring the phasediterence between said .self-oscillator waves Vand said radiated pulsesignals, and servo motive means controlling said phase shifting means inresponse .to said phase measuring .means for maintaining Ysaidgate-signals concurrent withA said received pulsetsignals.

5. Afradio noise-reducing system operating to eliminate `fnoise thatisdisplaced :in time with respect to received Vpulse signals, comprisingmeans for producing `gate signals having substantially the same durationas said freceived signals, utilization means activated b1/Said of saidgateand received signals andser-vo motive means.

for controlling saifdl phase shifting meansfin response to the timepositionof saidreceived signals,

6. A radio system comprising tmeans for transmitting periodic pulsesignals, means for receivingsaid .signals after a 4time delay, yaselfoscillator :for yprbducing Waves of a frequency substantially thesame as said 'received signals, means for generating gate signals having.substantially [the same duration as saidV received' signals, meansactivated by said 'gate signals for synchronizing the phase of .saidYself-oscillator waves 'to that of .said received signals, .delayingmeans for adjusting the,rela tive time positionof said.`gateand receivedsignals, and means controlling said delaying kmeans in accordance withlthe `time position of said se'lfaoscillat-or Waves for maintaining saidgate and received signals concurrent.

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M mi

